1. Field of the Invention
The present invention relates to a zoom lens and an image pickup apparatus, such as a video camera, a monitoring camera, a digital still camera, and a broadcasting camera, having the zoom lens.
2. Description of the Related Art
In recent years, a monitoring camera with high functionality and small size has been required. To that end, it is desirable that a photographic optical system to be used in the monitoring camera has higher functionality and smaller size than conventional photographical optical systems.
Examples of functions desired from a photographic optical system include, but are not limited to, having a large-diameter to provide a bright optical system, being able to capture an image even in low illumination environments, having a wide angle of view and a high zoom ratio, and being able to zoom on an object along the entire zoom range.
Japanese Patent Application Laid-Open No. 2009-205055 discusses a two-unit zoom lens including a first lens unit having negative refractive power and a second lens unit having positive refractive power in order from an object side to an image side. Japanese Patent Application Laid-Open No. 2009-230122 discusses a three-unit zoom lens including a first lens unit having negative refractive power, a second lens unit having positive refractive power, and a third lens unit having negative refractive power in order from an object side to an image side.
In a negative-lead type of zoom lens in which a lens unit arranged closest to an object side has negative refractive power, it is relatively easy to reduce the diameter of a front lens. Therefore, the configuration of the negative-lead type of zoom lens is advantageous to realizing a small-sized zoom lens with a wide angle of view.
The zoom lenses discussed in Japanese Patent Application Laid-Open No. 2009-205055 and Japanese Patent Application Laid-Open No. 2009-230122 have an F-number at a wide-angle end of about 2.85, a photographing angle of view at the wide-angle end of about 130 degrees, and a zooming ratio of about 2.1. However, these zoom lenses do not fully satisfy the demand to cause the monitoring camera to be more functional.